\begin{tikzpicture}
  \matrix [draw,row sep={1cm,between origins},column sep=5mm,rounded corners] at (0,0) 
  {
    \node [inner sep=0pt] (up1) {中间代码}; & \node [draw, rounded corners=0] (up2) {目标生成}; & \node [inner sep=0pt] (up3) {目标代码}; \\
    & \node [draw, rounded corners=0] (down2) {符号表}; \\
  };

  \draw [-Latex, thick] (up1.east) -- (up2.west);
  \draw [-Latex, thick] (up2.east) -- (up3.west);
  % \coordinate (d1) at ($(down2.north west)!0.333!(down2.north east)$);
  % \coordinate (d2) at ($(down2.north west)!0.666!(down2.north east)$);
  \draw [-Latex, thick] ([xshift=-.6em]up2.south) -- ([xshift=-.6em]down2.north);
  \draw [-Latex, thick] ([xshift=.6em]down2.north) -- ([xshift=.6em]up2.south);
\end{tikzpicture}